Abstract
In the former report of experimental studies on the control of Tyrophagus putrescentiae in straw mats with various pesticides, it has been found that the installation of paper sheets impregnated with fenthion or fenitrothion, covering the entire upper and lower surfaces of tatami (straw mats), has seemed to be most effective and economical. The experiments reported here were carried out to determine suitable concentration of the pesticides to be impregnated to the paper sheets and their chronic toxicities. It is considered in these experiment that the sheets impregnated with 0.25%, 1.0% and 5.0% fenthion at rate of 100ml per square meter effective at least for 3 to 6 months, 6 to 8 months and more than a year, respetively. The paper sheets imprenated with fenitrothion seem to be effective for 2 months at concentration of 0.25%, for 4 months at 1% and 7 months at 5%. Results in the toxicological tests indicated that mice exposed continuously for 93 days to the sheets treated with 5% fenitrothion and 0.25% fenthion were not showed any adverse effects as compared with untreated ones. Although the sheets impregnated with 25% fenitrothion and 5% and 1% fenthion gave some toxicities to the mice exposed, these sheets were less toxic to the mice than two kinds of paper sheets which have been used practically for three to four years without any adverse effects to the occupants in the dwellings in Japan.
